The invention relates to an apparatus for towing sea-going vessels, and more particularly it relates to linkages for utilization during the towing by pushing, and to skegs for utilization during the towing by pulling, of non-propelled barges by tugboats.
Non-propelled barges are powered through the water by either pushing the barge from the stern by a tugboat or by pulling the barge at the end of a line connected between the stern of the tugboat and the bow of the barge. The former method is usually accomplished by connecting the tugboat to the stern of the barge by a suitable linkage such as is illustrated in Applicant's U.S. Pat. No. 3,568,621, U.S. Pat. No. 4,407,214, and U.S. Pat. No. 4,326,479, which are incorporated by reference. The combined vessels then act effectively as one and navigation is accomplished through controls on the tugboat.
Barges pulled on a line, however, are free to oscillate from side-to-side around a vertical axis of rotation (yaw). If the amplitude of oscillation is small, then the condition is not serious. At times, though, a yawing barge can swing in a path having a width two to three times the length of the barge. Such substantial yawing has been known to capsize tugboats and even barges. To overcome this problem, skegs may be included on non-motorized barges wherein towing of the barge by pulling is anticipated. (Skegs are fin-like protrusions, usually attached as a parallel pair to the stern of the barge, which have a substantially vertical orientation and which are substantially aligned with the path of travel). While skegs help to reduce yawing drastically, they also offer additional water resistance.
Hence, to provide an improved apparatus for towing barges, both by pushing and by pulling, it is desirable to provide a device which adequately connects the tug to the barge when the barge is pushed and which functions as a stabilizing skeg to reduce yawing of the barge when it is pulled, and which minimizes water resistance in both cases.
Where the barge is pushed by a tugboat, prior tugboat and barge linkages have usually allowed freedom of movement for relative pitching, heaving and rolling. Such movement was generally permitted because it was believed to be advantageous to allow the tugboat to exhibit such independent response relative to the barge. It has been found, however, that in many instances the relative rolling, i.e. independent rotation around an axis along the centerline of the vessels, should be reduced to a bare minimum. When complete freedom of rolling is allowed, the tug often sustains excessive roll far beyond an acceptable range during steering.
There have been proposals to overcome the problem of relative rolling by means of a truss reinforced frame extending rearwardly from a barge and attaching directly to either side of the tugboat. Such an arrangement, however, requires a highly rugged construction.
It has further been proposed to provide mating surfaces, such as a barge having a stern recess to receive the bow of a tugboat as shown in Applicant's U.S. Pat. No. 3,568,621, in order to minimize roll. While such an arrangement is effective to preclude or inhibit rolling of the tugboat relative to the barge, the required surface area for the mating surfaces must be large because of the many variables which determine where the mating surfaces will contact. That is, the relationship between the surfaces is dependent upon the draft of each vessel, the pitching of the barge, the pitching of the tugboat, and the pivotal motion of the linkage, whether due to heaving or pitching of either of the vessels. The combination of all of these relative motions may therefore require, for example, a large slot in the barge stern with a suitable mating protrusion at the bow of the tugboat for a tugboat-barge combination, similar to that shown in applicant's patent, U.S. Pat. No. 3,568,621.
To provide an improved linkage for barges and tugboats, wherein it is desired to push a non-propelled barge by a tugboat, applicant previously conceived of a series of devices which eliminated the need for extended mating surfaces in the stern of the barge, one which provided readily defined mating surfaces, and one which lessened the strength requirements of the linkage structure. A number of such devices are shown in applicant's U.S. Pat. No. 4,407,214. That patent disclosed a rearwardly extending linkage frame pivotally secured to the stern of the barge along a substantially horizontal axis generally parallel to the stern of the barge. The linkage defined a recess generally facing the bow of the tugboat. Means were provided for aligning the bow or a member of the bow of the tugboat with a recess in the rear face of the linkage such that roll of the tugboat relative to the barge was minimized. Additionally, the apparatus disclosed in that patent included a means for securing the tugboat to the linkage such that freedom of movement for pitching and heaving of the tugboat relative to the barge is permitted. While the devices shown in U.S. Pat. No. 4,407,214 operated to properly restrict the freedom of relative motion between the tugboat and the barge, the devices generally continued to require mating surfaces on the tugboat, and they adversely increased the water resistance exerted against the tugboat and linkage.
Hence, to provide an improved apparatus for barges which may be towed by both pushing and pulling, it is desirable to provide a device which minimizes both water resistance and rolling of the barge relative to the tugboat while allowing freedom of movement for relative pitching and heaving, without requiring extended mating surfaces on either the barge of the tugboat.
One partial approach to lessening water resistance is shown in applicant's U.S. Pat. No. 4,326,479, which discloses the use of a flow flap positioned between the stern of the barge and the bottom rear edge of a linkage. This arrangement creates a continuous surface between the barge and the tugboat hull in order to lessen water resistance between the barge and the tugboat when the barge was pushed. It also requires, however, an elongated mating slot in the stern of the barge and a corresponding mating member at the bow of the tugboat. It is therefore desirable to provide an apparatus which minimizes water resistance without the provision of elongated slots and mating members.
It is further desirable to provide a linkage device which may alternatively function as a stabilizing skeg to reduce yawing of the barge when it is pulled, while providing minimized water resistance when the barge is either pushed or pulled.
It is also desirable to provide a device which allows safe pedestrian passage between the tugboat and the barge, and which allows reliable transfer of fluids between the tugboat and the barge, regardless of the relative draft and the relative motions of the two vessels.
It is still further desirable that the skeg portions be easily moved from their inward position, for use during barging pushing, to their outward position, for use as stabilizing skegs during barge pulling.